linux-kernel - Re: [PATCH v5 2/3] tracing: Add trace_total_entries() / trace_total_entries

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Message-ID: <20190319112537.5yi7gelkk4ixswmu@holly.lan>
Date:   Tue, 19 Mar 2019 11:25:37 +0000
From:   Daniel Thompson <daniel.thompson@...aro.org>
To:     Douglas Anderson <dianders@...omium.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>,
        Ingo Molnar <mingo@...hat.com>,
        Jason Wessel <jason.wessel@...driver.com>,
        kgdb-bugreport@...ts.sourceforge.net,
        Brian Norris <briannorris@...omium.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5 2/3] tracing: Add trace_total_entries() /
 trace_total_entries_cpu()

On Mon, Mar 18, 2019 at 01:47:40PM -0700, Douglas Anderson wrote:
> These two new exported functions will be used in a future patch by
> kdb_ftdump() to quickly skip all but the last few trace entries.
> 
> Suggested-by: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
> 
> Changes in v5: None
> Changes in v4:
> - trace_total_entries() / trace_total_entries_cpu() new for v4
> 
> Changes in v3: None
> 
>  kernel/trace/trace.c | 65 ++++++++++++++++++++++++++++++++++----------
>  kernel/trace/trace.h |  3 ++
>  2 files changed, 53 insertions(+), 15 deletions(-)
> 
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index ccd759eaad79..7afc90f82e53 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -3490,34 +3490,69 @@ static void s_stop(struct seq_file *m, void *p)
>  	trace_event_read_unlock();
>  }
>  
> +static void
> +get_total_entries_cpu(struct trace_buffer *buf, unsigned long *total,
> +		      unsigned long *entries, int cpu)
> +{
> +	unsigned long count;
> +
> +	count = ring_buffer_entries_cpu(buf->buffer, cpu);
> +	/*
> +	 * If this buffer has skipped entries, then we hold all
> +	 * entries for the trace and we need to ignore the
> +	 * ones before the time stamp.
> +	 */
> +	if (per_cpu_ptr(buf->data, cpu)->skipped_entries) {
> +		count -= per_cpu_ptr(buf->data, cpu)->skipped_entries;
> +		/* total is the same as the entries */
> +		*total = count;
> +	} else
> +		*total = count +
> +			ring_buffer_overrun_cpu(buf->buffer, cpu);
> +	*entries = count;
> +}
> +
>  static void
>  get_total_entries(struct trace_buffer *buf,
>  		  unsigned long *total, unsigned long *entries)
>  {
> -	unsigned long count;
> +	unsigned long t, e;
>  	int cpu;
>  
>  	*total = 0;
>  	*entries = 0;
>  
>  	for_each_tracing_cpu(cpu) {
> -		count = ring_buffer_entries_cpu(buf->buffer, cpu);
> -		/*
> -		 * If this buffer has skipped entries, then we hold all
> -		 * entries for the trace and we need to ignore the
> -		 * ones before the time stamp.
> -		 */
> -		if (per_cpu_ptr(buf->data, cpu)->skipped_entries) {
> -			count -= per_cpu_ptr(buf->data, cpu)->skipped_entries;
> -			/* total is the same as the entries */
> -			*total += count;
> -		} else
> -			*total += count +
> -				ring_buffer_overrun_cpu(buf->buffer, cpu);
> -		*entries += count;
> +		get_total_entries_cpu(buf, &t, &e, cpu);
> +		*total += t;
> +		*entries += e;
>  	}
>  }
>  
> +unsigned long trace_total_entries_cpu(struct trace_array *tr, int cpu)
> +{
> +	unsigned long total, entries;
> +
> +	if (!tr)
> +		tr = &global_trace;

This function is only ever called with tr set to NULL which means tr is
an argument looking for a user.

I wouldn't mind except if this was following copying prior art to keep
the API feel the same but I can't find any other trace function where
the trace_array can be substituted for NULL. AFAICT all the existing
sites where global_trace is used will use it unconditionally.


> +
> +	get_total_entries_cpu(&tr->trace_buffer, &total, &entries, cpu);
> +
> +	return entries;
> +}
> +
> +unsigned long trace_total_entries(struct trace_array *tr)
> +{
> +	unsigned long total, entries;
> +
> +	if (!tr)
> +		tr = &global_trace;

Ditto.


Daniel.


> +
> +	get_total_entries(&tr->trace_buffer, &total, &entries);
> +
> +	return entries;
> +}
> +
>  static void print_lat_help_header(struct seq_file *m)
>  {
>  	seq_puts(m, "#                  _------=> CPU#            \n"
> diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
> index d80cee49e0eb..4562b30eda9d 100644
> --- a/kernel/trace/trace.h
> +++ b/kernel/trace/trace.h
> @@ -719,6 +719,9 @@ void trace_init_global_iter(struct trace_iterator *iter);
>  
>  void tracing_iter_reset(struct trace_iterator *iter, int cpu);
>  
> +unsigned long trace_total_entries_cpu(struct trace_array *tr, int cpu);
> +unsigned long trace_total_entries(struct trace_array *tr);
> +
>  void trace_function(struct trace_array *tr,
>  		    unsigned long ip,
>  		    unsigned long parent_ip,
> -- 
> 2.21.0.225.g810b269d1ac-goog
>